Differentially cross-linked article and process for making the same



0 United States Patent n 3,542,077 [72] inventor Richard W. Muehmore3,199,541 8/1965 Richitelli 138/129 Redwood City, California 3,379,2184/1968 Conde 138/99 [21] Appl. No. 731,200 3,455,336 7/1969 Ellis 138/99[22] Filed I May 22,1968 3,455,337 7/1969 Cook 138/178 [45] PatentedNov. 24,1970 a [73] Assignee Rayehetn Corporation 532:: i z ggzz g'laudon Menlo Park, California y y y a corporation of California [54]DIFFERENTIALLY CROSS-LINKED ARTICLE AND 1ff$2f,?," ABSTRACT: Adifferentially cross-linked polymeric article having an Insert embeddedtherein, the article on one side of U.S. CI- th i t t i i ffi i nt osJinked density to be sub. 138/170 8 61/401 161/139 stantially infusibleand on the other side of the insert being a [161/166 substantiallyfusible and noncross-linked. The article is [51] Int. Cl. F161 11/00 f bi t d by extruding, molding or otherwise positioning the [50] Field ofSearch 138/178, insert within a po|ymeric -5 and the" cmss |inking the172, 174,99, 170; 16l/39,40, 139, 166,213, 2 material on the one side ofthe insert, the insert preventing cross-linking of the material on theother side. The article may [56] cued then be imparted with the propertyof elastic memory so as to UNITED STATES PATENTS render it heatrecoverable. Several specific embodiments of 3,189,509 6/1965 Needham161/39 such an article are disclosed.

Patented Nov. 24, 1970 3 3,542,077

FIG. 1.

INVENTOR. E/("HAED 1 14 MUCH/V/flff BY a 7% mrrnnEN'ri-ALLY cnossrlnrosn ARTICLE AND PROCESS ron MAKING rap SAME BACKGROUND OF THEINVENTION the same. According to the Cook application, the disclosure ofwhich is incorporated'by reference herein, a differentially cross-linkedarticle, that is,'one which has a first portion containing sufficientcross-link density to be substantially infusible and a secondportion'which is substantially fusible and noncross-linkei can befabricated by irradiating the article in a manner such that the outerportion absorbs substantially all of the total incident radiation while.the inner portion remains essentially unaffected. Among the factors tobeconsidered in achieving the differential cross-linking are the-nature ofthe material of the article and its thickness and the energy level andtype of irradiating source used. As disclosed in the Cook application,the irradiation source can bemodified by wrapping the article to beirradiated in aluminum foil ofcalculated thickness to reduce the maximumenergy of the electrons of an electron beam.

SUMMARY OF THE INVENTION According to thepresent invention, anothermethod isprovided'for producing a differentially cross-linked polymericarticle. lnstead of depending on the properties of the polymericmaterial itself, or on a shielding .introduced between the materialandthe irradiating source, an insert is embedded within the polymericmaterial and serves to prevent the portion of. the article which itoverlies from being cross-linked when the article is irradiated orotherwise treated. The resulting article has a substantially infusibleportion and a substantially fusible portion, the line of demarcationbetween the por tions being marked by, the insert; The insert inaddition may serve a function completely unrelated to its shieldingfunction,

for example, as a reinforcing member for the article. In the main, thisdescription will be'directed to a process and resulting article wherethe cross-linking isaccomplished by irradiation. It should beunderstood, however, that this is for purposes of illustration only andthat other methods of cross-linking fall within the scope of theinvention.

A particular example where such an insert serves a function above andbeyondits shielding function isin'the fabrication of a heatrecove'rableclosure system. Other types of such closure systems aredisclosed in U.S. -Pat: application Ser. No. 475,742, now U.S. Pat. Ser.No. r 3,379,218; filed June 29,

1965 by Julian S. Conde and entitledfClosure Sleevefor Pipes or theLike, and Ser. No. 506,l6l,:-now U.S. Pat. Ser.

No. 3,455,336, filed Nov."3, 1965'by Rogerl-IrEllisand entitledHeat-Recoverable Article and Process, the disclosures of theseapplications being incorporated by reference herein.

In each of these applications, a longitudinally split heat recoverablemember is provided with mechanical means for fastening the split edgesof the sleeve together andmaintaining them in that relationship duringand after heat recovery of the member. While the constructions disclosedin these applications have been'fo'und to be generally satisfactory,they each require the use of anadhesive or sealing compound to form aseal where the edges of the sleeveoverlap in order to assure acompletely sealed closure.

Accordingto the present invention, a closure member is provided in whichthe inserts are, or may be made, hookshaped so that they can be used tointerconnect the edges of the sleeve after it'has been longitudinallysplit. The inserts also serve to shield portions .of the member fromirradiatiomso that these portions are not cross-linked and are fusibleat the heat recovery temperature of the sleeve; Consequently, theseportions being fusible and subject to the recovery'forces, fuse underpressure and heat'and form a seal along the length of a the sleeveduring heat recovery thereof.

one side of theinsert substantially infusible and on the other side ofthe insert substantially fusible.

It is also an object of the present invention to provide a method forfabricating such anarticle.

It is another object of the present invention to provide a heatrecoverable member which may be formed into a closed tubular member andheat recovered while maintaining its tubular shape.

' It is another object of the present invention to provide such a methodwherein sealing is accomplished without the use of any externalsealingmaterial. 1

These and other objects and advantages of the present invention willbecome more apparent upon reference to the accompanying description anddrawingslin which:

BRIEF DESCRIPTION OF THE DRAWINGS a mechanical interconnection has beenmade;

FIG. 6 shows in cross section the interconnection after the article hasbeen heat recovered; and

FIGS. 7, 8 and-9 are cross-sectional views showing another modificationof the closure system according to the presentinvention. I

DESCRIPTION OF THE INVENTION In FIG. 1 there is shown a tubular member 6constructed in accordance with the present invention. The member 6comprises an outer portion 7, an insert Sand an inner portion 9., theportions 7 and 9 preferably, but not necessarily being of thesame-polymeric material. The member 6.ca'n be formed in anyco'nventionalmanner such as molding or extruding, and if the latter is used, canbethe product of a compound extrusion. or may be formed by first extrudingthe inner portion 9, then positioning the insert 8 thereover and'thenextruding the portion 7 over the insert 8. The member'6 is then exposedto radiation sufficient to provide the portion 7 with a sufficientcross-link density, such that it is substantially infusible. Thepresence of the insert 8', which serves as a shield orirradiationattenuator, results in the portion 9 being substantially not crosslinked and'substantially fusible.

The irradiation can be of various types including charged particles,i.e., beta and alpha, neutral particles, i.e., neutrons, andelectromagnetic, that is, -gamma,sand ultraviolet. As will be obvious to.those skilled in the art, the absorption behavior of these different,types of irradiation in a material will vary and must be taken intoaccount'in practicing this invention; While the member 6 is shown asbeing tubular, it should be'understood that this illustrative only andnot restrictive. The member could assume any desired shape, for example,it could simply be a flat slab of polymeric material with an insertembedded therein. it is' also within the scope of the present inventiontoprovide the shield with a lesser area than the polymeric material. sothat only parts of the article are differentially cross-linked.

Any polymeric material capable of being cross'linked by the variousconventional treatments, such as irradiation, may be utilized in thepresent invention. Preferably, the polymeric polyvinylidene fluoride;cross-linked ethylene vinyl acetate copolymers; crossdlinkedethyleneethyl aerylate copolymers; cross-linked polyamides; etc. The polymericmaterials used in the practice of this invention may contain additivessuch as flame retarders, plasticizers, fillers and other additivesfamiliar to those skilled in the art.

The insert 8 may be of any suitable material, either plastic or metal,that will act to sufficiently attenuate the radiation so as to preventthe cross-linking of the portion 9 of the member 6. Metals that can beused include almost any material that can be formed into a thin sheet,for example, steel, copper, bronze, aluminum, etc. Many plastics canalso be used, their appropriateness being determined partially by thepurpose for which the member 6 is designed, and for which the insert 8is provided. For example, if the article is to be heat recoverable (inwhich case, of course, the insert cannot be complete and continuous asshown in FIG. 1) plastics that can be used include thermoset materialsuch as epoxies, polyesters, melamines, diallyl phthalates, etc., eitheras filled materials or unfilled. Thermoplastic materials of high meltingpoints such as nylon, polycarbonate, chlorinated polyether,polyphenyloxide, etc. again, either filled or unfilled, can be used withheat unstable materials of low melting points such as polyethylene,plasticized polyvinylchloride, ethylene vinyl acetate copolymers,ethylene ethyl acrylate copolymers, polyvinylidene fluoride, etc. In thecase of a heat recoverable part, the insert, either metal or plastic,must be unaffected by the heat necessary to shrink the part, or affectedin such small degree that it will not unduly deform when subjected tothe recovery forces generated by the shrinking and pulling of thesleeve.

As will be obvious, an article constructed in accordance with thepresent invention will be useful in many different applications. As hasalready been pointed out, one such use is as a heat recoverable closuremember for pipes or the like. A first embodiment of such a closuremember is shown in FIGS. 2 through 6, while a second embodiment is shownin FIGS. 7 through 9. 1 1

1n the embodiment shown in FIGS. 2 through 6, a sleeve 10 is extruded,molded or otherwise'formed with a pair of internal loops 11 and 12forming a pair of openings 13 and 14. The loop 11 is continuous, whilethe loop 12 is formed with a gap 15. Each of the loops 1! and 12 isprovided with inserts in the nature of interconnecting members or hooks16 and 17 that are sufficiently strong to withstand the shrinkage forcesexerted during heat recovery and that are unaffected by the heatnecessary to shrink the part or at least affected in such small degreethat they will not unduly deform when subjected to heat and the recoveryforces. The inserts l6 and 17 are preferably flexible enough so thatthey can be flexed in the longitudinal direction sufficiently to permitthe sleeve 10 to be positioned over an irregular article, for example, acurved piece of pipe.'These inserts may be constructed of the materialsspecified above.

After the sleeve 10 with its inserts l6 and 17 have been formed, it isirradiated as discussed above. The inserts 16 and 17 must be unaffectedor not substantially affected by the irradiation process, andpreferably, are of such thickness that they will attenuate the radiationso that the material on the inner surfaces of the loops at 11 and 12,namely, the surfaces 18 and 19 of the loop 11 and the surfaces 20 and 21of the loop 12 are not cross-linked and are substantially fusible whilethe remaining areas of the sleeve 10 are cross-linked to a density torender them substantially infusible.

Once the sleeve 10 has been differentially cross-linked, it is capableof having the property of heat recoverability imparted to it. This canbe accomplished by several techniques. In one way, the differentiallycross-linked tube can be heated by radiant heat, hot fluids or othermeans, and then subjected to a differential pressure between the insideand outside of the tubing; the amount of pressure being sufficient'tocause the tube to expand in a controlled fashion. When the tube hasreached the desired size and shape, it is cooled. The cooling causes thereformation of strong interchain forces such as crystallinity which setsthe tubing in the expanding state since at low temperatures these forcesare stronger than those due to crosslinks. Reheating substantiallyweakens the interchain forces and the cross-link forces become dominantand the tubing recovers to its original cross-linked geometry.Alternately, the

property of heat recoverability may be imparted by plastically deformingthe differentially cross-linked tubing at temperatures at which theinterchain forces are still appreciable to magnitude. This can beaccomplished by the application of a substantial amount of pressurewhich can be acquired mechanically or hydraulically. The tubing willthen retain this shape and can be recovered elastically by heating to atemperature above the crystalline melting point or softening range ofthe polymer employed, leaving the cross-links to force the tubing toassume its original cross-linked geometry. In any event, the tubing thatis prepared is heat recoverable so that at any time the tubing may beshrunk to approximately its original diameter simply by the applicationof heat.

Preferably, thc'tubing is expanded in the manner disclosed in the USPat. to Cook et al. No. 3,086,242, the disclosure of which isincorporated herein by reference. The Cook et al. Pat. also disclosesvarious materials that are particularly suitable for this purpose. Inaddition to the materials specified above and in the Cook et al. Pat,noncrystalline polymeric materials exhibiting the property of plastic orelastic memory, such as polyurethane, ionmers, etc., could also be usedin practicing the present invention. Since the articles of the presentinvention can be made from material of either plastic or elasticmemory,'the terms elastic memory" and plastic memory are usedinterchangeably'and are intended to be mutually inclusive.

After the sleeve 10 has been expanded and cooled, it is slit along itslength between the loops 11 and 12 as shown at 22 in FIG. 4. A sectionof the wall of sleeve 10 overlying the loop 11 is also removed to form agap 23. If desired, this gap 23 could be formed during the molding forextrusion process. FIG. 5 shows the sleeve after the interlocking hastaken place. As can be seen, the surface 19 of the loop 11 is adjacentto and in contact with surface 24 of the loop 12 while the surface 18 ofthe loop 11 is in contact with the surface 21 of the loop 12. When thesleeve is heated to its heatrecovery temperature, it attempts toreturn-to its original configuration with the result that it will shrinkdown tightly over any object having a dimension greater than the initialdimension of the sleeve. The edges of the sleeve are prevented frombeing pulled apart by the recovery forces by the hooklike inserts 16 and17 which are sufficiently strong to withstand these forces. Since thesurfaces 18, 19, 21 and 24 of the loops 11 and 12 have not beencross-linked, they are substantially fusible at the recovery temperatureof the sleeve with the result that they are rendered fusible by the heatand are pressed together by the recovery forces of the main body of thesleeve. This combination of heat and force fuses/the surfaces,eliminating any interface and forming one continuous material. When thesleeve cools, the wall is continuous and'sealed into a complete cylinderwithout any adhesive interface at any point. The weaknesses of anadhesive system are thereby eliminated and a truly seamless tubing madefrom a wrap around sleeve results. This is shown in FIG. 6.

An alternate construction of a closure sleeve according to the presentinvention is shown in FIGS. 7, 8 and 9. A sleeve 30 is molded, extrudedor otherwise formed with inserts 31 and 32, the insert 31 beingpositioned within a loop 33 as was the case in the previous embodimentwhile theinsert 32 follows the contour of the wall of the sleeve 30. Thesleeve is irradiated and then expanded. The insert 32 must be of a metalor thermoset or thermoplastic material that can be formed afterirradiation and expansion into a hook-shape as shown at 34 in FIG. 8 andwhich will retain this shape during heat recovery of the sleeve 30. Aswas the case in the previous embodiment, a gap 35 is formed in theportion of the sleeve 30 overlying the loop 33, so that the hook 34 canbe inserted therein as shown in FIG. 9. The surfaces 36, 37, 38 and 39could also be used, in particular, solid state cross-linking in which across-linkingagent, or system of cross-linking agents, is diffused intothe shaped polymeric article from either the liquid or gaseous statewould be appropriate to the practice of the present invention. In such acase, the insert, rather than acting as a radiation shield would act asa barrier to the diffusing cross-linking agents and would prevent thevolume of the polymeric material'below the insert from beingcross-linked. Of course, the parameters of the diffusion would have tobe controlled so that itwould not be long enough to cause the diffusingagents to be able tomovelaterally across the undersurface of the insertand thus cross-link the polymeric material in that area. In any event,-some incursions along the edge of the insert or shield would be expected,but there nevertheless would remain large areas where the polymericmaterial was noncross-linked and hence fusible at elevated temperatures.The diffusion of thecross-linking agents would, of course, have to beeffected fro'm'only one side of the insert in order for it to act as abarrier. if the article in question was tubular such as that shown inFIG. '1, the diffusion could be accomplished by passing thetubular-member after it was extruded or otherwise formed through a bathof the diffusing agent, the term bath being used to include the agent ineither the liquid or gaseous state. Of course, the diffusing agent wouldbe prevented from access to the interior of the tubing. If the polymericarticle was in the form of a slab or the like, a suitable fixture ormask would be used to limit access of the crosslinking agent to thedesired surface of the article. Examples of processes and materials thatcould be used for such solid state cross-linking can be found in U.S.application Ser. No. 502,413, now U.S. Pat. Ser. No. 3,386,949, filed onOct. 22, i965 by Edward C. Stivers entitled Chemical Crosslinking In TheSolid State and Ser. No. 544,099, filed Apr. 21, 1966 by Norman Thorpentitled Cross-linkedPolyamides the disclosures of which areincorporated by reference herein.

1 It should be understood that the inserts illustrated are onlyexemplary and that various other forms of inserts could be used. ifdesired, inserts such as those shown may be slitted partly through atintervals along their lengths to provide additional flexibility to thesleeves where the objects to be covered have irregular shapes. v Theinvention may be embodied in other specific forms not departing from thespirit or' central characteristics thereof. The present embodiments aretherefore to be considered in all respects as illustrative and notrestrictive, the scope of the invention being indicated by the appendedclaims rather than by the foregoing description, and all changes whichcome within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

IQ'A differentially cross-linked. polymeric article having a wall, aninsert embedded in said wall, said wall on one side of said insertcontaining sufficient cross-linked density to be substantially infusibleand on the other side of said insert being substantially'noncross-linkedand substantially fusible.

2. A differentiallyirradiated, heat recoverable cross-linkedpolymeric'article having a wall in which is'embedded a radiationattenuating insert, said wall on one side of said insert containingsufficient cross-linked density to be substantially infusible and on theothersidc of said insert being fusible and substantiallynoncross-linked, said wall having the property of elastic memory.

3. A heat recoverable closure member adapted to be heat recovered ontoan object comprising: a piece of material which has been dimensionallychanged from an original heat stable form to an independently heatunstable form capable of moving in the direction of its original form .non the application 0 heat alone, said piece of material aving first andsecondedges which can be brought together to form a tubular member; saidpiece of material having a first integral interconnecting means at saidfirst edge and a second integral interconnecting means at saidsecondedge, said first and second interconnecting means being cooperable toselectively engage or disengage said edges with one another, each ofsaid interconnecting means including an insert embedded in saidmateriaLsaid insert being substantially unaffected by heat sufficient tocause heat recovery of said piece of material and capable of maintainingsaid edges together during heat recovery of said piece of materialaround said object.

4. The closure member of claim 3, wherein portions of said material atsaid interconnecting means are fusible at the heat recovery temperatureof said material. 7

' 5. The closure member of claim 4, wherein said material is a polymer,said portions being uncross-linked and the remainder being cross-linked.

6. The closure member of claim 4, wherein said portions are locatedbetween said inserts are interconnected.

7. The closure member'of claim 6, wherein said portions when saidinterconnecting means form a seal between said edges when said piece ofmaterial is heat recovered.

8. The closure member of claim 3, wherein said inserts are hook-shaped.

